Composite RF tag, and tool mounted with the composite RF tag

ABSTRACT

The present invention relates to a composite RF tag for transmitting and receiving information using an electromagnetic induction method, comprising a magnetic antenna mounted with an IC, and a resin layer formed around the magnetic antenna, wherein the magnetic antenna comprises a central core formed of a magnetic material and a coil-shaped electrode material disposed around the core. The RF tag according to the present invention comprises the magnetic antenna surrounded by the resin, and therefore can provide a composite magnetic RF tag which can minimize adverse influence by surrounding water or metals in view of maintenance of tools or parts to which the composite RF tag is mounted, and is free from occurrence of any failure or cracking.

This application is a divisional of application Ser. No. 13/260,988filed Nov. 21, 2011, now allowed, which is the U.S. national phase ofInternational Application No. PCT/JP2010/55196 filed 25 Mar. 2010 whichdesignated the U.S. and claims priority to JP 2009-088129 filed 31 Mar.2009, the entire contents of each of which are hereby incorporated byreference.

TECHNICAL FIELD

The present invention relates to a composite RF tag for informationcommunication using a magnetic field component. The composite RF tag ofthe present invention comprises a magnetic antenna mounted with an ICand a resin disposed around the magnetic antenna, whereby adverseinfluence of not only surrounding water but also surrounding metals oncommunication characteristics thereof can be minimized. In addition,there can be provided a composite magnetic RF tag which is free fromfracture and cracking.

BACKGROUND ART

An antenna for transmitting and receiving an electromagnetic wave usinga magnetic material (hereinafter referred to merely as a “magneticantenna”) in which a magnetic field component coming from outside isallowed to pass through a core (magnetic material), around which a coilof a conductive wire is wound, to convert the magnetic field componentinto a voltage (or current) induced by the coil, has been widely used insmall sized radios and TVs. Such a magnetic antenna is also used in anon-contact object identification device called an RF tag which hasrecently widely come into use.

To transmit and receive an electromagnetic wave with a higher frequency,a planar loop coil which is free of a magnetic material and has a coilsurface parallel to an object to be identified is used as an antenna inRF tags. When the frequency is much higher (UHF band or microwave band),an electric field antenna (dipole antenna or dielectric antenna) fordetecting an electric field component instead of a magnetic fieldcomponent is widely used in such RF tags.

However, the planar loop antenna and electric field antenna have thefollowing problems. That is, when such an antenna comes close to ametallic object, an image (mirror effect) is generated on the metallicobject. Since the image has a phase opposite to that of the antenna, thesensitivity of the antenna tends to be lost.

On the other hand, there is also known a magnetic antenna fortransmitting and receiving a magnetic field component which comprises amagnetic layer as a central core, an coil-shaped electrode materialwound on the core, an insulating layer formed on one or both outsidesurfaces of the core on which the coil-shaped electrode material isprovided, and a conductive layer formed on one or both outside surfacesof the insulating layer (Patent Document 1). The magnetic antennadescribed in Patent Document 1 can maintain properties required forantennas even when coming into contact with metal articles. There arealso known tags or magnetic antennas which are installed under specificconditions (Patent Document 2).

Further, it is conventionally known that, in RF tags for transmittingand receiving information using an electromagnetic induction method,surrounding water, if any, has adverse influence thereon, i.e., causesincrease in dielectric constant around the RF tags, resulting indeviation of resonance frequency of the RF tags and thereforedeterioration in communication characteristics thereof.

PRIOR ARTS Patent Documents

-   Patent Document 1: Japanese Patent Application Laid-open (KOKAI) No.    2007-19891-   Patent Document 2: Japanese Patent Application Laid-open (KOKAI) No.    2002-207980

SUMMARY OF THE INVENTION Problem to be Solved by the Invention

In the methods described in Patent Documents 1 and 2, there have beenproposed some measures which are taken against the applications in whichthe magnetic antenna and RF tag are attached to metals in the specificdirections. However, in these methods, no sufficient measures againstadverse influence of water are taken into consideration. Further, inthese methods, no sufficient measures are taken against occurrence offracture and cracking when the magnetic antenna and RF tag are attachedto metallic or plastic parts.

Also, in the case of RF tags of an inlay (inlet) type which have been ingeneral widely spread, a base film used therein tends to hardlywithstand a high temperature such as about 100° C. or higher whensubjected to injection molding process, etc. The other processes thanthe above injection molding process such as hot melt process,heat-curing process and UV curing process may also be used for producingthe above RF tags. However, these processes tend to be unsuitable forproduction of the RF tags of an inlay (inlet) type because they have arisk of increase in temperature used therein.

Under these circumstances, an object of the present invention is toprovide a composite RF tag comprising a magnetic antenna or a compositemagnetic antenna which can be minimized in deterioration ofcommunication characteristics and is free from occurrence of fractureand cracking even when attached to metallic or plastic parts or tools orwhen used in environmental conditions in which a large amount ofsurrounding water is present.

Means for Solving the Problem

The above object or technical task of the present invention can beachieved by the following aspects of the present invention.

That is, in accordance with the present invention, there is provided acomposite RF tag for transmitting and receiving information using anelectromagnetic induction method, comprising a magnetic antenna mountedwith an IC, and a resin, wherein the resin is disposed to surround themagnetic antenna and has a thickness of not less than 200 μm (Invention1).

Also, according to the present invention, there is provided a compositeRF tag for transmitting and receiving information using anelectromagnetic induction method, comprising a magnetic antenna mountedwith an IC, and a resin, wherein the magnetic antenna has a hexahedralshape and comprises a central core formed of a magnetic material and acoil-shaped electrode material disposed around the core, and the resinis disposed to surround the magnetic antenna and has a thickness of notless than 200 μm (Invention 2).

Also, according to the present invention, there is provided thecomposite RF tag as described in the above Invention 1 or 2, wherein theresin is a polyamide resin, an epoxy resin, a polyimide resin, aurethane rein, a polyolefin resin, an acrylic resin or a mixture of anytwo or more of these resins (Invention 3).

In addition, according to the present invention, there is provided atool comprising the composite RF tag as described in any one of theabove Inventions 1 to 3 (Invention 4).

Effect of the Invention

The composite RF tag according to the present invention is free from notonly deterioration in communication characteristics thereof but also arisk of occurrence of fracture or cracking even when attached tometallic or plastic parts or even when used under environmentalconditions in which a large amount of surrounding water is present, andtherefore can be suitably used in the applications such as 13.56 MHzRFID.

The composite RF tag according to the present invention has a small sizeand a high toughness, and is less influenced by outside environments, inparticular, metals, conductive materials or water which are presentoutside of the composite RF tag, and therefore can be used in variousapplications in which the composite RF tag is attached or fitted to asurface or recess of portable equipments, containers, metallic parts,substrates (boards), metallic tools, various metal molds, printingplates, printing rolls, vehicles such as bicycles and automobiles,metallic jigs, markers for bolts or rivets, etc., or can be used inenvironmental conditions where a large amount of surrounding water ispresent, or in water.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a conceptual view showing a composite RF tag according to thepresent invention.

FIG. 2 is a conceptual view showing a magnetic antenna used in thepresent invention.

FIG. 3 is a conceptual view showing a magnetic antenna used in thepresent invention.

FIG. 4 is a conceptual view showing a magnetic antenna used in thepresent invention.

FIG. 5 is a view showing a laminated structure of a coil portion of amagnetic antenna used in the present invention.

FIG. 6 is a conceptual view showing a magnetic antenna used in thepresent invention.

FIG. 7 is a conceptual view showing a magnetic antenna used in thepresent invention.

FIG. 8 is a conceptual view showing a magnetic antenna used in thepresent invention.

FIG. 9 is a conceptual view showing a laminated structure of a magneticantenna used in the present invention.

FIG. 10 is a conceptual view showing a laminated structure of a magneticantenna used in the present invention.

FIG. 11 is a graph showing a relationship between a thickness of a resinin a composite RF tag according to the present invention and a rate ofreduction in communication distance thereof.

EXPLANATION OF REFERENCE NUMERALS

1: Through-hole; 2: electrode layer (coil electrode); 3: core; 4: coil;4-1: minimum unit of coil; 4-2: coil open end; 5: magnetic layer; 6:insulating layer; 7: conductive layer; 8: non-magnetic layer; 9: IC chipconnecting terminal; 10: IC chip; 11: capacitor connecting electrode;12: capacitor; 17: magnetic antenna; 20: resin

PREFERRED EMBODIMENT FOR CARRYING OUT THE INVENTION

First, the composite RF tag according to the present invention isdescribed.

In the composite RF tag according to the present invention, a resinlayer is formed around the magnetic antenna mounted with an IC (RF tag)along a longitudinal direction of a coil thereof (opened end of magneticflux). The magnetic antenna comprises a central core formed from amagnetic material or from a magnetic material and a non-magneticmaterial, and a coil-shaped electrode material disposed around the core.The IC is mounted to the magnetic antenna to form an RF tag.

The composite RF tag according to the present invention is schematicallyshown in FIG. 1.

As shown in FIG. 1, the composite RF tag according to the presentinvention has such a structure in which a resin (20) is disposed so asto surround a peripheral portion of the magnetic antenna (17). However,the shape of the composite RF tag according to the present invention isnot particularly limited to a rectangular parallelopiped shape or acylindrical shape as shown in FIG. 1, and the composite RF tag may alsohave an optional shape such as a polygonal prism shape, a polygonalpyramid shape, a conical shape and a spherical shape. The term “(theresin) surrounding (the magnetic antenna)” as used herein is intended toinclude all of structures in which a resin is present around themagnetic antenna, for example, the structure in which the magneticantenna is embedded in a molded product of the resin, the structure inwhich the magnetic antenna is coated with the resin in the form of acoating film, etc.

In the present invention, the thickness of the resin surrounding themagnetic antenna is not less than 200 μm even at a thinnest portionthereof. When the thickness of the resin is less than 200 μm, theresulting composite RF tag tends to be deteriorated in communicationsensitivity by adverse influence of water when attached with water orused in water. The thickness of the resin in the composite RF tag ispreferably not less than 250 μm.

The resin layer used in the present invention may be formed of variousresins. Examples of the resins include polystyrene resins, acrylonitrilestyrene resins, acrylonitrile butadiene styrene resins, acrylic resins,polyethylene resins, polypropylene resins, polyamide resins, polyimideresins, polyacetal resins, polycarbonate resins, vinyl chloride resins,modified polyphenylene ether resins, polybutylene terephthalate resins,polyphenylene sulfide resins, epoxy resins, urethane resins, polyolefinresins, silicone resins, and mixtures of these resins.

Next, the magnetic antenna used in the present invention is described.The shape of the magnetic antenna used in the present invention is notparticularly limited, and may be a hexahedral shape such as a cubicshape and a rectangular parallelopiped shape, a polygonal prism shape, acylindrical shape or a generally U-shape. Among these shapes, preferredis a hexahedral shape such as a cubic shape and a rectangularparallelopiped shape.

In FIGS. 2 to 4, there are shown schematic views of the magnetic antennaused in the present invention.

The magnetic antenna used in the present invention as shown in FIG. 2has a basic structure which comprises a magnetic layer (core) as acentral body, a coil-shaped (wire winding-shaped) electrode materialdisposed around the central core, and an insulating layer formed on oneor both outside surfaces of the core on which the coil-shaped electrodematerial is provided.

In the present invention, the magnetic antenna as shown in FIG. 2comprises a magnetic layer (5) in the form of a single layer or alaminated layer comprising a plurality of magnetic layers which may berespectively obtained by forming a mixture of magnetic particles and abinder into a sheet shape as shown in FIG. 5. Then, a desired number ofthrough-holes (1) are formed through the thus formed magnetic layer (5).Next, the electrode material is poured into the respectivethrough-holes, and further an electrode layer (2) formed of theelectrode material is formed on both surfaces of the magnetic layerwhich surfaces are perpendicular to the through-holes, to thereby form acoil such that the magnetic layer (5) constitutes a core having a prismshape or a rectangular shape. In this case, there is obtained such aconstruction in which both terminal ends of the magnetic layer (5)constituting the coil (4) are open ends of a magnetic circuit.

Next, insulating layers (6) are respectively formed on upper and lowersurfaces of the coil (4) on which the electrode layer is formed.

The thus obtained sheet is cut into a desired shape along thethrough-holes (1) and the open ends (3) of the coil and then integrallycalcined, or is integrally calcined and then cut into a desired shapealong the through-holes (1) and the open ends (3) of the coil, therebyproducing the magnetic antenna (LTCC technology).

The magnetic antenna used in the present invention as shown in FIG. 3has a basic structure which comprises a magnetic layer (core) as acentral body, a coil-shaped (wire winding-shaped) electrode materialdisposed around the central core, an insulating layer formed on one orboth outside surfaces of the core on which the coil-shaped electrodematerial is provided, and a conductive layer formed on one or bothoutside surfaces of the insulating layer.

The core may have a structure in which a magnetic material constitutingthe core is divided into plural parts by a non-magnetic material asshown in FIG. 4 or FIG. 6.

In the magnetic antenna used in the present invention, the structure inwhich the magnetic core is divided into plural parts by the non-magneticmaterial may be of any configuration as long as the magnetic material isdivided by the non-magnetic material when viewed in a section of thecore which is cut in the direction perpendicular to a magnetic fluxpassing through the magnetic antenna. For example, there may beillustrated the structures as shown in FIG. 6( a) to FIG. 6( d).

The magnetic antenna used in the present invention as shown in FIG. 4has a basic structure which comprises a central core comprising themagnetic material (5) and the non-magnetic material (8), a coil-shaped(wire winding-shaped) electrode material disposed on an outside of thecentral core, and an insulating layer formed on one or both outsidesurfaces of the core on which the coil-shaped electrode material isprovided. The core has such a structure in which the magnetic materialis divided into plural parts by the non-magnetic material.

Meanwhile, in the magnetic antenna shown in FIG. 4, the area ratio ofall portions of the magnetic material to all portions of thenon-magnetic material (all portions of the magnetic material/allportions of the non-magnetic material) as measured on the section of thecore is preferably not more than 1.0. When the area ratio of theportions formed of the non-magnetic material exceeds the above-specifiedrange, the content of the magnetic material in the core is reduced,which tends to be disadvantageous for achieving reduction in size of themagnetic antenna. The area ratio of all portions of the magneticmaterial to all portions of the non-magnetic material as measured in thesection of the core is more preferably not more than 0.5, and still morepreferably not more than 0.2.

Meanwhile, in the magnetic antenna shown in FIG. 4, the ratio of asectional area (S) of one of the magnetic layers forming the core of themagnetic antenna to a length (L) of the magnetic antenna (S/L) as shownin FIG. 6 is preferably not more than 0.3. When the area ratio (S/L) ismore than 0.3, it may be difficult to reduce adverse influences owing toa demagnetizing field.

In the present invention, the magnetic antenna having the core as shownin FIG. 4 may be produced, for example, by the following method.

First, a mixture prepared by mixing magnetic particles and a binder isformed into a sheet shape to form a single magnetic layer or a pluralityof magnetic layers in the form of a laminated layer.

Separately, a mixture prepared by mixing non-magnetic particles and abinder is formed into a sheet shape to form a single non-magnetic layeror a plurality of non-magnetic layers in the form of a laminated layer.

Next, as shown in FIG. 6, the magnetic layers (5) and the non-magneticlayers (8) are alternately laminated to obtain a laminate having adesired total thickness.

Then, a desired number of through-holes (1) are formed through the thusobtained laminated layer comprising the magnetic layers and thenon-magnetic layers. The electrode material is poured into therespective through-holes. Also, the electrode material is applied onboth surfaces of the laminated layer which are perpendicular to thethrough-holes, to form an electrode layer (2) in the form of a coil(wire winding) which is connected with the electrode material pouredinto the through-holes. The electrode material poured into thethrough-holes and the electrode layer cooperate so as to form a coilsuch as a rectangular core is constituted from the magnetic layers. Inthis case, there is obtained such a construction in which both terminalends of the magnetic layers constituting the core are open ends of amagnetic circuit.

Next, as shown in FIG. 4, insulating layers (6) are respectively formedon upper and lower surfaces of the coil on which the electrode layer isprovided.

The thus obtained sheet is cut into a desired shape along thethrough-holes and the open ends of the coil and then integrallycalcined, or is integrally calcined and then cut into a desired shapealong the through-holes and the open ends of the coil, thereby producingthe magnetic antenna (LTCC technology).

As shown in FIG. 7 and FIG. 8, the magnetic antenna (17) used in thepresent invention may also have a basic structure which comprises acentral core (3) formed of a magnetic material and a coil-shaped (wirewinding-shaped) electrode material disposed outside of the core (3) toform a plurality of coils (4-1) around the core, wherein a plurality ofthe coils (4-1) are electrically connected in parallel to each other anddisposed in series on the same core (3) (although the number of thecoils shown in FIG. 7 and FIG. 8 is four, the number of the coils usablein the present invention is not particularly limited thereto).

The inductance L₁ of the respective coils (4-1) of the magnetic antennahaving the above structure satisfies the following relational formula(1) when the IC is mounted to the magnetic antenna.L ₁·1/(4π²×(operating frequency)²×(capacity of IC+parasitic capacity ofantenna))  <Relational formula (1)>

When the inductance L₁ of the respective coils (4-1) of the magneticantenna is capable of satisfying the above relational formula (1), theresulting magnetic antenna can be further enhanced in communicationsensitivity. The inductance L₁ of the respective coils (4-1) of themagnetic antenna is preferably not less than 2 times and more preferablynot less than 3 times the combined inductance L₀ of the magneticantenna.

The combined inductance L₀ of the magnetic antenna having the abovestructure satisfies the following relational formula (2) when the IC ismounted to the magnetic antenna.L ₀·1/(4π²×(operating frequency)²×(capacity of IC+parasitic capacity ofantenna))  <Relational formula (2)>

When the combined inductance L₀ of the magnetic antenna is capable ofsatisfying the above relational formula (2), the resonance frequency ofthe RF tag to which the IC is mounted can be readily adjusted to itsoperating frequency, and can be further enhanced in communicationsensitivity thereof. The magnetic antenna capable of satisfying theabove relational formula (2) may be produced by controlling a magneticpermeability of a material forming the core, the number of winding ofthe coils, a sectional area of the coils, a length of the coils, etc.

In addition, as schematically shown in FIG. 9, in the magnetic antennaused in the present invention, a capacitor electrode (11) may also beprovided on one or both outside surfaces of the insulating layers (6)which are disposed on an upper surface and a lower surface of the coil(4) to sandwich the coil (4) therebetween.

Meanwhile, in the magnetic antenna used in the present invention asschematically shown in FIG. 9, a parallel electrode or an interdigitalelectrode may also be formed by printing as the capacitor to be formedon an upper surface of the insulating layer. In addition, the capacitormay be connected in parallel or in series to the coil lead terminal.

Further, as schematically shown in FIG. 10, the insulating layer may befurther provided on its outside surface where the capacitor electrode(11) is provided, with an additional insulting layer (6). In addition,an electrode layer (9) which also serves as an IC chip connectingterminal may be further formed on an outside surface of the thus formedinsulating layer (6) such that the insulating layer (6) is sandwichedtherebetween to form a capacitor which may be connected in parallel orin series to the IC chip terminal.

In addition, as shown in FIG. 8, in the magnetic antenna used in thepresent invention, the terminal (9) capable of being connected with theIC chip (10) may be formed on an upper surface of the insulating layer(6). Meanwhile, the IC chip connecting terminal (9) and the coil leadterminal may be connected in parallel or in series to each other, andthen integrally calcined.

In the magnetic antenna used in the present invention, as the magneticmaterial of the core, there may be used Ni—Zn-based ferrite, etc. TheNi—Zn-based ferrite used in the present invention preferably has acomposition comprising 45 to 49.5 mol % of Fe₂O₃, 9.0 to 45.0 mol % ofNiO, 0.5 to 35.0 mol % of ZnO and 4.5 to 15.0 mol % of CuO. The ferritecomposition may be suitably selected such that the resulting core as themagnetic material has a high magnetic permeability and a low magneticloss in a frequency band to be used. When using a material having aexcessively high magnetic permeability as the magnetic material of thecore, the resulting core tends to suffer from an increased magnetic lossand as a result, tends to be unsuitable for antennas.

For example, the ferrite composition is preferably selected such thatthe core has a magnetic permeability of 70 to 120 at 13.56 MHz when themagnetic antenna is applied to an RFID tag, and has a magneticpermeability of 10 to 30 at 100 MHz when the magnetic antenna is used toreceive commercial FM broadcasts, because the magnetic loss can bereduced.

In the magnetic antenna used in the present invention, as thenon-magnetic material of the core, there may be used non-magneticferrites such as Zn-based ferrite, glass-based ceramic materials such asborosilicate glass, zinc glass and lead glass, or mixtures comprisingthe non-magnetic ferrite and the glass-based ceramic material at anadequate mixing ratio.

The ferrite powder used as the non-magnetic ferrite may be selected soas to have such a Zn-based ferrite composition that a sintered body ofthe ferrite powder has a volume resistivity of not less than 10⁸ Ω·cm.The Zn-based ferrite composition preferably comprises 45 to 49.5 mol %of Fe₂O₃, 17.0 to 22.0 mol % of ZnO and 4.5 to 15.0 mol % of CuO.

The glass-based ceramic powder used as the glass-based ceramic materialmay be selected so as to have such a composition that its linearexpansion coefficient is not largely different from that of the magneticmaterial used. More specifically, the composition is preferably selectedsuch that the difference in linear expansion coefficient between theglass-based ceramic powder and a soft magnetic ferrite used as themagnetic material lies within the range of ±5 ppm/° C.

Next, the process for producing the composite RF tag according to thepresent invention is described.

The composite RF tag according to the present invention is formed suchthat the magnetic antenna mounted with the IC which is produced by theabove method is surrounded by the resin.

As the method of forming the resin around the magnetic antenna, theremay be used ordinary forming methods such as an injection moldingmethod, a compression molding method, an extrusion molding method, a hotmelt method, a UV curing method, a powder coating method and an impastocoating method.

For example, after fitting the RF tag in a metal mold, the molten resinis poured into the metal mold to coat the RF tag therewith, and thensolidified, thereby producing the composite RF tag comprising anintegrated body comprising the RF tag and the resin.

In addition, the composite RF tag according to the present invention maybe used or constructed such that the RF tag is embedded into variousresin molded products. For example, the composite RF tag of the presentinvention may be used in such a configuration as embedded into variouscontainers, packing materials or containers, transporting facilities,boxes, substrates (boards), medical equipments, tools and stationeries.

<Function>

The magnetic antenna according to the present invention can be minimizedin deterioration of communication characteristics and is free fromfracture or cracking even when placed in such a state as attached tometallic or plastic parts or when used under environmental conditions inwhich a large amount of surrounding water is present, and therefore canbe suitably applied to tools or parts with a good maintenance thereof.

EXAMPLES

In the followings, the present invention is described in more detail onthe basis of preferred embodiments thereof by referring to theaccompanying drawings. However, these preferred embodiments are onlyillustrative and not intended to limit the present invention thereto.

[RF Tag 1]

In order to form a magnetic layer, 100 parts by weight of precalcinedNi—Zn—Cu ferrite particles which had been found to have a magneticpermeability of 100 as a magnetic material at 13.56 MHz after sinteringat 900° C. (Fe₂O₃: 48.5 mol %; NiO: 25 mol %; ZnO: 16 mol %; CuO: 10.5mol %), 8 parts by weight of a butyral resin, 5 parts by weight of aplasticizer, and 80 parts by weight of a solvent were mixed in a ballmill to prepare a slurry. The resulting slurry was applied on a PET filmby a doctor blade to form a coating layer with a size of 150 mm×150 mmsuch that the thickness of the coating layer obtained after sinteringwas 0.1 mm, thereby forming a sheet.

In order to form an insulating layer, 100 parts by weight of precalcinedZn—Cu ferrite particles (Fe₂O₃: 48.5 mol %; ZnO: 41 mol %; CuO: 10.5 mol%), 8 parts by weight of a butyral resin, 5 parts by weight of aplasticizer, and 80 parts by weight of a solvent were mixed in a ballmill to prepare a slurry. The resulting slurry was applied on a PET filmby a doctor blade to form a coating layer with the same size andthickness as those of the sheet for the magnetic layer, thereby forminga sheet.

Next, as shown in FIG. 5, through-holes (1) were formed through the thusobtained green sheet for the magnetic layer and filled with an Ag paste.In addition, an Ag paste was printed on both surfaces of the green sheetwhich surfaces are perpendicular to the through-holes (1). Ten sheets ofthe thus prepared magnetic layers were laminated on one another to forma coil.

Next, as shown in FIG. 2, the green sheets for the insulating layer (6)were respectively laminated on upper and lower surfaces of the coil (4).The thus laminated green sheets were bonded together by applying apressure thereto. The resulting laminate was cut along the lines passingthrough the through-holes and the coil open ends (3), and integrallycalcined at 900° C. for 2 hr, thereby obtaining a magnetic antenna (1)with a size of 10 mm in width×3 mm in length which had a coil windingnumber of 23 turns (in these figures, the coil winding number is shownin a simplified manner, and only the three magnetic layers are shown asbeing laminated for the sake of simplicity. The other drawings are alsoshown in the same way).

Further, an IC for an RF tag was connected to both ends of the coil ofthe magnetic antenna, and a capacitor was connected in parallel to theIC. Then, the resonance frequency was adjusted to 13.56 MHz, therebyobtaining an RF tag.

The thus obtained RF tag was loaded in an injection molding machine, andmolded together with a polypropylene resin such that the resulting resincoat had a thickness of 1000 μm, thereby obtaining a composite RF tag 1.

[Methods for Measuring and Adjusting Resonance Frequency]

The resonance frequency was determined from a peak frequency ofimpedance as measured by an impedance analyzer “4291A” manufactured byAgilent Technology Co., Ltd.

[Method for Measuring Communication Distance]

The communication distance was determined from a maximum distancebetween a reader/writer (product name “TR3-A201/TR3-C201” manufacturedby Takaya Co., Ltd.) as an antenna and the above obtained composite RFtag at which they were able to still communicate with each other at13.56 MHz.

To evaluate the communication distance in water, the composite RF tagwas placed in a container filled with water, and the container wasallowed to move toward and away from the antenna to vary the distancetherebetween and measure the maximum distance therebetween at which theantenna and the composite RF tag were able to still communicate witheach other.

[RF Tag 2]

The magnetic antenna produced in the same manner as defined in RF tag 1was subjected to a hot melt molding process together with apolyamide-based resin such that the resulting resin coat had a thicknessof 500 μm, thereby obtaining a composite RF tag 2.

[RF Tag 3]

The magnetic antenna produced in the same manner as defined in RF tag 1was subjected to a UV curing process together with an acrylic UV-curingresin such that the resulting resin coat had a thickness of 200 μm,thereby obtaining a composite RF tag 3.

[RF Tag 4: Comparative Example]

The magnetic antenna produced in the same manner as defined in RF tag 1was directly mounted with an IC, and a resonance frequency thereof wasadjusted to 13.56 MHz while maintaining the magnetic antenna as such,thereby obtaining an RF tag 4.

[RF Tag 5: Comparative Example]

The magnetic antenna produced in the same manner as defined in RF tag 1was coated with an epoxy-based resin such that the resulting resin coathad a thickness of 20 μm, thereby obtaining a composite RF tag 5.

[RF Tag 6: Comparative Example]

The magnetic antenna produced in the same manner as defined in RF tag 1was coated with a polyimide-based resin such that the resulting resincoat had a thickness of 50 μm, thereby obtaining a composite RF tag 6.

[RF Tag 7: Comparative Example]

The magnetic antenna produced in the same manner as defined in RF tag 1was coated with an epoxy-based resin such that the resulting resin coathad a thickness of 100 μm, thereby obtaining a composite RF tag 7.

TABLE 1 Rate of reduction in Examples Thickness Resonance communicationand Comp. of resin Communication frequency distance in Examples coat(μm) distance (mm) (MHz) water (%) RF tag 1 1000 60 13.6    0% RF tag 2 500 60 13.6    0% RF tag 3  200 60 13.6    0% RF tag 4   0 60 13.6 −44%(Comp. Example) RF tag 5  20 60 13.6 −30% (Comp. Example) RF tag 6  5060 13.6 −15% (Comp. Example) RF tag 7  100 60 13.6  −5% (Comp. Example)

As shown in Table 1, even when coated with the resin, the obtainedcomposite RF tag could maintain a good performance similar to those ofComparative Examples, and was free from deterioration in communicationcharacteristics even in the state immersed in water, as well as fromfracture and cracking.

INDUSTRIAL APPLICABILITY

The composite RF tag according to the present invention has a small sizeand a high toughness, and is less influenced by outside environments, inparticular, metals, conductive materials or water which are presentoutside of the composite RF tag, and therefore can be used in variousapplications in which the composite RF tag is attached or fitted to asurface or recess of portable equipments, containers, metallic parts,substrates (boards), metallic tools, various metal molds, printingplates, printing rolls, vehicles such as bicycles and automobiles,metallic jigs, markers for bolts or rivets, etc., or can be used inenvironmental conditions in which a large amount of surrounding water ispresent, or in water.

The invention claimed is:
 1. A composite RF tag for transmitting andreceiving information using an electromagnetic induction method,comprising a magnetic antenna mounted with an IC, and a resin, whichresin is disposed to surround the magnetic antenna and has a thicknessof not less than 200 μm, and which magnetic antenna comprises a centralcore formed of a magnetic material and a coil-shaped electrode materialdisposed around the core, which magnetic antenna has a hexahedral shape.2. A composite RF tag according to claim 1, wherein the resin is apolyamide resin, an epoxy resin, a polyimide resin, a urethane resin, apolyolefin resin, an acrylic resin or a mixture of any two or more ofthese resins.
 3. A tool comprising the composite RF tag as defined inclaim 1.